As puzzleannie said, if you are responsible for this someone in your parish should be training you.
In the Ordinary Form Mass the altar is very easy to dress:
At least two candles, on or near the altar
A crucifix if there is none near the altar.
Anything more is usually added at the Offertory and in our parish it's done thus:
Missal to the left, priest will adjust it to suit himself,
Corporal centered along the width and close to the edge on the side where the priest stands.
Chalice and purificator placed to the right of the corporal. If there is no Offertory Procession the paten or ciborium with the unconsecrated bread is placed near the chalice.
Anything else is usually brought in the Offertory procession and/or by the altar servers (ciborium, bread, wine, water, purificators, lavabo bowl, finger towels)